The present invention relates to a system for injecting a fluid, such as water or a water solution, into internal combustion engines and, more specifically, to a fluid injection system and method for injecting fluid into spark-ignition engines in which the injection rate is proportional to the engine speed and engine load.
Various cooling fluids, such as water and water in solution with other substances, such as methanol or alcohol, have been commonly injected into hydrocarbon engines, both of the spark-ignition and compression-ignition type, to provide improved engine operation. The fluid absorbs heat within the combustion chamber and provides for an even burning rate to prevent, or at least greatly minimize, detonation of the fuel charge in the combustion chamber. In addition, the fluid tends to diminish the accumulation of carbon deposits within the combustion chamber and, because the combustion process takes place at a generally lower temperature, inhibits the formation of high-temperature pollutants, specifically the oxides of nitrogen (NO.sub.x).
Various types of prior devices have been used to introduce cooling fluids into the intake air of internal combustion engines. These devices have included nozzle-type injectors in which the fluid is pumped directly into the engine and intake air humidifiers in which air is passed through a volume of water before being introduced into the engine. However, since the injection of a relatively low volume of fluid is desired when compared to the volume of fuel/air mixture introduced into the engine, it is difficult, if not impossible, to meter the fluid with the precision needed to insure optimum performance when it is pumped directly into the engine. Also, if humidified air is used, much less heat absorption is obtained when compared to water, since the humidified air has a lower density than dry air with water droplets.
These prior devices suffer from additional problems, since they are usually operated solely in response to engine speed, or by the exhaust gases from the engine, either directly or as modified by the engine intake manifold pressure. Although these techniques result in a fluid injection rate that may be adequate under certain engine operating conditions, such as a constant-speed cruise condition, the injection rate during other engine operating conditions, such as acceleration and deceleration, may be too little or too much. When the fluid injection rate is insufficient, the beneficial effects of the cooling fluid are, of course, not obtained. Conversely, when the injection rate is too high, the surplus fluid within the combustion chamber tends to quench the combustion process and, of course, diminish engine performance.